Method and system for charging multi-cell lithium-based batteries

ABSTRACT

A method and system for charging multi-cell lithium-based batteries. In some aspects, a battery charger includes a housing, at least one terminal to electrically connect to a battery pack supported by the housing, and a controller operable to provide a charging current to the battery pack through the at least one terminal. The battery pack includes a plurality of lithium-based battery cells, with each battery cell of the plurality of battery cells having an individual state of charge. The controller is operable to control the charging current being supplied to the battery pack at least in part based on the individual state of charge of at least one battery cell.

RELATED APPLICATIONS

The present patent application is a continuation of prior filedco-pending U.S. patent application Ser. No. 11/837,190, filed on Aug.10, 2007, which is a continuation of prior filed co-pending U.S. patentapplication Ser. No. 11/322,782, filed on Dec. 30, 2005, now U.S. Pat.No. 7,262,580, issued on Aug. 28, 2007, which is a divisional of priorfiled U.S. patent application Ser. No. 10/719,680, filed on Nov. 20,2003, now U.S. Pat. No. 7,176,654, issued on Feb. 13, 2007, which claimsthe benefit of prior filed U.S. provisional patent application Ser. No.60/428,358, filed on Nov. 22, 2002; Ser. No. 60/428,450, filed on Nov.22, 2002; Ser. No. 60/428,452, filed on Nov. 22, 2002; Ser. No.60/440,692, filed Jan. 17, 2003; Ser. No. 60/440,693, filed on Jan. 17,2003; Ser. No. 60/523,716, filed on Nov. 19, 2003; and Ser. No.60/523,712, filed on Nov. 19, 2003, the entire contents of all of whichare hereby incorporated by reference. The entire content of U.S. patentapplication Ser. No. 10/720,027, filed on Nov. 20, 2003, now U.S. Pat.No. 7,157,882, issued on Jan. 2, 2007, is also hereby incorporated byreference.

FIELD OF THE INVENTION

The present invention generally relates to a method and system forbattery charging and, more particularly, to a method and system forpower tool battery charging.

BACKGROUND OF THE INVENTION

Cordless power tools are typically powered by portable battery packs.These battery packs range in battery chemistry and nominal voltage andcan be used to power numerous tools and electrical devices. Typically,the battery chemistry of a power tool battery is either Nickel-Cadmium(“NiCd”) or Nickel-Metal Hydride (“NiMH”). The nominal voltage of thebattery pack usually ranges from about 2.4 V to about 24 V.

SUMMARY OF THE INVENTION

Some battery chemistries (such as, for example, Lithium (“Li”),Lithium-ion (“Li-ion”) and other Lithium-based chemistries) requireprecise charging schemes and charging operations with controlleddischarge. Insufficient charging schemes and uncontrolled dischargingschemes may produce excessive heat build-up, excessive overchargedconditions and/or excessive overdischarged conditions. These conditionsand build-ups can cause irreversible damage to the batteries and canseverely impact the battery's capacity.

The present invention provides a system and method for charging abattery. In some constructions and in some aspects, the inventionprovides a battery charger capable of fully charging various batterypacks with different battery chemistries. In some constructions and insome aspects, the invention provides a battery charger capable of fullycharging lithium-based batteries, such as, for example, lithium-cobaltbatteries, lithium-manganese batteries and spinel batteries. In someconstructions and in some aspects, the invention provides a batterycharger capable of charging Lithium-based chemistry battery packs ofdifferent nominal voltages or in different nominal voltage ranges. Insome constructions and in some aspects, the invention provides a batterycharger having various charging modules that are implemented based ondifferent battery conditions. In some constructions and in some aspects,the invention provides a method and system for charging a lithium-basedbattery by applying pulses of constant current. The time between pulsesand the length of the pulses may be increased or decreased by thebattery charger depending on certain battery characteristics.

Independent features and independent advantages of the invention willbecome apparent to those skilled in the art upon review of the followingdetailed description, claims, and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a battery.

FIG. 2 is another perspective view of a battery, such as the batteryshown in FIG. 1.

FIG. 3 is a perspective view of a battery, such as the battery shown inFIG. 1, electrically and physically connected to a battery charger.

FIG. 4 is a schematic view of a battery electrically connected to abattery charger, such as the battery and battery charger shown in FIG.3.

FIGS. 5 a and 5 b are flowcharts illustrating operation of a batterycharger embodying aspects of the invention, such as the battery chargershown in FIG. 3.

FIG. 6 is a flowchart illustrating a first module capable of beingimplemented on a battery charger embodying aspects of the invention,such as the battery charger shown in FIG. 3.

FIG. 7 is a flowchart illustrating a second module capable of beingimplemented on a battery charger embodying aspects of the invention,such as the battery charger shown in FIG. 3.

FIG. 8 is a flowchart illustrating a third module capable of beingimplemented on a battery charger embodying aspects of the invention,such as the battery charger shown in FIG. 3.

FIG. 9 is a flowchart illustrating a fourth module capable of beingimplemented on a battery charger embodying aspects of the invention,such as the battery charger shown in FIG. 3.

FIG. 10 is a flowchart illustrating a fifth module capable of beingimplemented on a battery charger embodying aspects of the invention,such as the battery charger shown in FIG. 3.

FIG. 11 is a flowchart illustrating a sixth module capable of beingimplemented on a battery charger embodying aspects of the invention,such as the battery charger shown in FIG. 3.

FIG. 12 is a flowchart illustrating a charging algorithm capable ofbeing implemented on a battery charger embodying aspects of theinvention, such as the battery charger shown in FIG. 3.

FIG. 13 is a schematic diagram of a battery electrically connected to abattery charger.

FIG. 14A-B are views of other constructions of a battery.

FIG. 15A-B are perspective views of a battery, such as one of thebatteries shown in FIGS. 1, 2, and 14A-B, electrically and physicallyconnected to a power tool.

FIG. 16 is a schematic view of the charging current for a battery.

FIG. 17 is another schematic diagram of a battery.

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. Also, it is to be understood thatthe phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having” and variations thereof herein ismeant to encompass the items listed thereafter and equivalents thereofas well as additional items.

DETAILED DESCRIPTION OF THE DRAWINGS

A battery pack or battery 20 is illustrated in FIGS. 1 and 2. Thebattery 20 is configured for transferring power to and receiving powerfrom one or more electrical devices, such as, for example, a power tool25 (shown in FIGS. 15A-B) and/or a battery charger 30 (shown in FIGS. 3and 4). In some constructions and in some aspects, the battery 20 canhave any battery chemistry such as, for example, lead-acid,Nickel-cadmium (“NiCd”), Nickel-Metal Hydride (“NiMH”), Lithium (“Li”),Lithium-ion (“L-ion”), another Lithium-based chemistry or anotherrechargeable battery chemistry. In some constructions and in someaspects, the battery 20 can supply a high discharge current toelectrical devices, such as, for example, a power tool, havinghigh-current discharge rates. In the illustrated constructions, thebattery 20 has a battery chemistry of Li, Li-ion or another Li-basedchemistry and supplies an average discharge current that is equal to orgreater than approximately 20 A. For example, in the illustratedconstruction, the battery 20 can have a chemistry of lithium-cobalt(“Li—Co”), lithium-manganese (“Li—Mn”) spinel, or Li—Mn Nickel.

In some constructions and in some aspects, the battery 20 can also haveany nominal voltage such as, for example, a nominal voltage ranging fromapproximately 9.6 V to approximately 50 V. In one construction (seeFIGS. 1-3), for example, the battery 20 has a nominal voltage ofapproximately 21 V. In another construction (see FIG. 14), the battery20A has a nominal voltage of approximately 28 V. It should be understoodthat, in other constructions, the battery 20 may have another nominalvoltage in another nominal voltage range.

The battery 20 includes a housing 35 which provides terminal supports40. The battery 20 further includes one or more battery terminalssupported by the terminal supports 40 and connectable to an electricaldevice, such as the power tool 25 and/or the battery charger 30. In someconstructions, such as, for example, the construction illustrated inFIG. 4, the battery 20 includes a positive battery terminal 45, anegative battery terminal 50 and a sense battery terminal 55. In someconstructions, the battery 20 includes more or fewer terminals than inthe construction shown.

The battery 20 includes one or more battery cells 60 each having achemistry and a nominal voltage. In some constructions, the battery 20has a battery chemistry of Li-ion, a nominal voltage of approximately 18V or 21 V and includes five battery cells. In some constructions, eachbattery cell 60 has a chemistry of Li-ion, and each battery cell 60 hassubstantially the same nominal voltage, such as, for example,approximately 3.6 V or approximately 4.2 V.

In some constructions and in some aspects, the battery 20 includes anidentification circuit or component electrically connected to one ormore battery terminals. In some constructions, an electrical device,such as, for example, a battery charger 30 (shown in FIGS. 3 and 4)would “read” the identification circuit or component or receive an inputbased on the identification circuit or component in order to determineone or more battery characteristics. In some constructions, the batterycharacteristics could include, for example, the nominal voltage of thebattery 20, the temperature of the battery 20 and/or the chemistry ofthe battery 20.

In some constructions and in some aspects, the battery 20 includes acontrol device, a microcontroller, a microprocessor or a controllerelectrically connected to one or more battery terminals. The controllercommunicates with the electrical devices, such as a battery charger 30,and provides information to the devices regarding one or more batterycharacteristics or conditions, such as, for example, the nominal voltageof the battery 20, individual cell voltages, the temperature of thebattery 20 and/or the chemistry of the battery 20. In someconstructions, such as, for example, the construction illustrated inFIG. 4, the battery 20 includes an identification circuit 62 having amicroprocessor or controller 64.

In some constructions and in some aspects, the battery 20 includes atemperature-sensing device or thermistor. The thermistor is configuredand positioned within the battery 20 to sense a temperature of one ormore battery cells or a temperature of the battery 20 as a whole. Insome constructions, such as, for example, the construction illustratedin FIG. 4, the battery 20 includes a thermistor 66. In the illustratedconstruction, the thermistor 66 is included in the identificationcircuit 62.

As shown in FIGS. 3 and 4, the battery 20 is also configured to connectwith an electrical device, such as a battery charger 30. In someconstructions, the battery charger 30 includes a housing 70. The housing70 provides a connection portion 75 to which the battery 20 isconnected. The connecting portion 75 includes one or more electricaldevice terminals to electrically connect the battery 20 to the batterycharger 30. The terminals included in the battery charger 30 areconfigured to mate with the terminals included in the battery 20 and totransfer and receive power and information from the battery 20.

In some constructions, such as, for example, the constructionillustrated in FIG. 4, the battery charger 30 includes a positiveterminal 80, a negative terminal 85 and a sense terminal 90. In someconstructions, the positive terminal 80 of the battery charger 30 isconfigured to mate with the positive battery terminal 45. In someconstructions, the negative terminal 85 and the sense terminal 90 of thebattery charger 30 are configured to mate with the negative batteryterminal 50 and the sense battery terminal 55, respectively.

In some constructions and in some aspects, the battery charger 30 alsoincludes charging circuitry 95. In some constructions, the chargingcircuitry 95 includes a control device, a microcontroller, amicroprocessor or a controller 100. The controller 100 controls thetransfer of power between the battery 20 and the battery charger 30. Insome constructions, the controller 100 controls the transfer ofinformation between the battery 20 and the battery charger 30. In someconstructions, the controller 100 identifies and/or determines one ormore characteristics or conditions of the battery 20 based on signalsreceived from the battery 20. Also, the controller 100 can controloperation of the charger 30 based on identification characteristics ofthe battery 20.

In some constructions and in some aspects, the controller 100 includesvarious timers, back-up timers and counters and/or can perform varioustiming and counting functions. The timers, back-up timers and countersare used and controlled by the controller 100 during various chargingsteps and/or modules. The timers, back-up timers and counters will bediscussed below.

In some constructions and in some aspects, the battery charger 30includes a display or indicator 110. The indicator 110 informs a user ofthe status of the battery charger 30. In some constructions, theindicator 110 can inform the user of different stages of charging,charging modes or charging modules that are beginning and/or beingcompleted during operation. In some constructions, the indicator 110includes a first light-emitting diode (“LED”) 115 and a second LED 120.In the illustrated construction, the first and second LEDs 115 and 120are different colored LEDs. For example, the first LED 115 is a red LED,and the second LED 120 is a green LED. In some constructions, thecontroller 100 activates and controls the indicator 110. In someconstructions, the indicator 110 is positioned on the housing 70 orincluded in the housing 70 such that the indicator 110 is visible to theuser. Display could also include an indicator showing percent charged,time remaining, etc. In some constructions, the display or indicator 110may include the fuel gauge provided on the battery 20.

The battery charger 30 is adapted to receive an input of power from apower source 130. In some constructions, the power source 130 isapproximately a 120-V AC, 60-Hz signal. In other constructions, thepower source 130 is, for example, a constant current source.

In some constructions and in some aspects, the battery charger 30 cancharge various rechargeable batteries having different battery chemistryand different nominal voltages, as described below. For example, in anexemplary implementation, the battery charger 30 can charge a firstbattery having a battery chemistry of NiCd and a nominal voltage ofapproximately 14.4 V, a second battery having a battery chemistry ofLi-ion and a nominal voltage of approximately 18 V, and a third batteryhaving a battery chemistry of Li-ion and a nominal voltage ofapproximately 28 V. In another exemplary implementation, the batterycharger 30 can charge a first Li-ion battery having a nominal voltage ofapproximately 21 V and a second Li-ion battery having a nominal voltageof approximately 28 V. In this exemplary implementation, the batterycharger 30 can identify the nominal voltages of each battery 20, andeither scale certain thresholds accordingly, as discussed below, ormodify voltage readings or measurements (taken during charging)according to the battery nominal voltage.

In some constructions, the battery charger 30 can identify the nominalvoltage of a battery 20 by “reading” an identification componentincluded in the battery 20 or by receiving a signal from, for example, abattery microprocessor or controller. In some constructions, the batterycharger 30 may include a range of acceptable nominal voltages forvarious batteries 20 that the charger 30 is able to identify. In someconstructions, the range of acceptable nominal voltages can include arange from approximately 8 V to approximately 50 V. In otherconstructions, the range of acceptable nominal voltages can include arange from approximately 12 V to approximately 28 V. In furtherconstructions, the battery charger 30 can identify nominal voltagesequaling about 12 V and greater. Also in further constructions, thebattery charger 30 can identify nominal voltages equaling about 30 V andlower.

In other constructions, the battery charger 30 can identify a range ofvalues that includes the nominal voltage of the battery 20. For example,rather than identifying that a first battery 20 has a nominal voltage ofapproximately 18 V, the battery charger 30 can identify that the nominalvoltage of the first battery 20 falls within the range of, for example,approximately 18 V to approximately 22 V, or approximately 16 V toapproximately 24 V. In further constructions, the battery charger 30 canalso identify other battery characteristics, such as, for example, thenumber of battery cells, the battery chemistry, and the like.

In other constructions, the charger 30 can identify any nominal voltageof the battery 20. In these constructions, the charge 30 can be capableof charging any nominal voltage battery 20 by adjusting or scalingcertain thresholds according to the nominal voltage of the battery 20.Also in these constructions, each battery 20, regardless of the nominalvoltage, may receive approximately the same amplitude of charge currentfor approximately the same amount of time (for example, if each battery20 is approximately fully discharged). The battery charger 30 can eitheradjust or scale the thresholds (discussed below) or adjust or scale themeasurements according to the nominal voltage of the battery 30 beingcharged.

For example, the battery charger 30 may identify a first battery havinga nominal voltage of approximately 21 V and 5 battery cells. Throughoutcharging, the battery charger 30 modifies every measurement that thecharger 30 samples (e.g., battery voltage) to obtain a per-cellmeasurement. That is, the charger 30 divides every battery voltagemeasurement by 5 (e.g., five cells) to obtain, approximately, theaverage voltage of a cell. Accordingly, all of the thresholds includedin the battery charger 30 may correlate to a per-cell measurement. Also,the battery charger 30 may identify a second battery having a nominalvoltage of approximately 28 V and 7 battery cells. Similar to theoperation with the first battery, the battery charger 30 modifies everyvoltage measurement to obtain a per-cell measurement. Again, all of thethresholds included in the battery charger 30 may correlate to aper-cell measurement. In this example, the battery charger 30 can usethe same thresholds for monitoring and disabling charging for the firstand second batteries, enabling the battery charger 30 to charge manybatteries over a range of nominal voltages.

In some constructions and in some aspects, the battery charger 30 basesthe charging scheme or method for charging the battery 20 on thetemperature of the battery 20. In one construction, the battery charger30 supplies a charging current to the battery 20 while periodicallydetecting or monitoring the temperature of the battery 20. If thebattery 20 does not include a microprocessor or controller, the batterycharger 30 periodically measures the resistance of the thermistor 66after predefined periods of time. If the battery 20 includes amicroprocessor or controller, such as controller 64, then the batterycharger 30 either: 1) interrogates the controller 64 periodically todetermine the battery temperature and/or if the battery temperature isoutside an appropriate operating range(s); or 2) waits to receive asignal from the controller 64 indicating that the battery temperature isnot within an appropriate operating range, as will be discussed below.

In some constructions and in some aspects, the battery charger 30 basesthe charging scheme or method for charging the battery 20 on the presentvoltage of the battery 20. In some constructions, the battery charger 30supplies a charging current to the battery 20 while periodicallydetecting or monitoring the battery voltage after predefined periods oftime when the current is being supplied to the battery 20 and/or whenthe current is not being supplied, as will be discussed below. In someconstructions, the battery charger 30 bases the charging scheme ormethod for charging the battery 20 on both the temperature and thevoltage of the battery 20. Also, charging scheme can be based onindividual cell voltages.

Once the battery temperature and/or battery voltage exceeds a predefinedthreshold or does not fall within an appropriate operating range, thebattery charger 30 interrupts the charging current. The battery charger30 continues to periodically detect or monitor the batterytemperature/voltages or waits to receive a signal from the controller 64indicating that the battery temperature/voltages are within anappropriate operating range. When the battery temperature/voltages arewithin an appropriate operating range, the battery charger 30 may resumethe charging current supplied to the battery 20. The battery charger 30continues to monitor the battery temperature/voltages and continues tointerrupt and resume the charging current based on the detected batterytemperature/voltages. In some constructions, the battery charger 30terminates charging after a predefined time period or when the batterycapacity reaches a predefined threshold. In other constructions,charging is terminated when the battery 20 is removed from the batterycharger 30.

In some constructions and in some aspects, the battery charger 30includes a method of operation for charging various batteries, such asthe battery 20, having different chemistries and/or nominal voltages. Anexample of this charging operation 200 is illustrated in FIGS. 5 a and 5b. In some constructions and in some aspects, the battery charger 30includes a method of operation for charging Li-based batteries, such asbatteries having a Li—Co chemistry, a Li—Mn spinel chemistry, a Li—MnNickel chemistry, and the like. In some constructions and in someaspects, the charging operation 200 includes various modules forperforming different functions in response to different batteryconditions and/or battery characteristics.

In some constructions and in some aspects, the method of operation 200includes modules for interrupting charging based on abnormal and/ornormal battery conditions. In some constructions, the charging operation200 includes a defective pack module, such as the defective pack moduleillustrated in flowchart 205 of FIG. 6, and/or a temperatureout-of-range module, such as the temperature out-of-range moduleillustrated in flowchart 210 of FIG. 7. In some constructions, thebattery charger 30 enters the defective pack module 205 in order toterminate charging based on abnormal battery voltage, abnormal cellvoltage and/or abnormal battery capacity. In some constructions, thebattery charger 30 enters the temperature out-of-range module 210 inorder to terminate charging based on abnormal battery temperature and/orone or more abnormal battery cell temperatures. In some constructions,the charging operation 200 includes more or fewer modules whichterminate charging based on more or fewer battery conditions than themodules and conditions discussed above and below.

In some constructions and in some aspects, the charging operation 200includes various modes or modules for charging the battery 20 based onvarious battery conditions. In some constructions, the chargingoperation 200 includes a trickle charge module, such as the tricklecharge module illustrated in flowchart 215 of FIG. 8, a step chargemodule, such as the step charge module illustrated in flowchart 220 ofFIG. 9, a fast charge module, such as the fast charge module illustratedin flowchart 225 of FIG. 10, and/or a maintenance charge module, such asthe maintenance module illustrated in flowchart 230 of FIG. 11.

In some constructions and in some aspects, each charging module 215-230is selected by the controller 100 during the charging operation 200based on certain battery temperature ranges, certain battery voltageranges and/or certain battery capacity ranges. In some constructions,each module 215-230 is selected by the controller 100 based on thebattery characteristics shown in Table 1. In some constructions, thecondition “battery temperature” or “temperature of the battery” caninclude the temperature of the battery taken as a whole (i.e., batterycells, battery components, etc.) and/or the temperature of the batterycells taken individually or collectively. In some constructions, eachcharging module 215-230 can be based on the same base charging scheme orcharging algorithm, such as, for example, a full charge current, asdiscussed below.

Operation for Charging Li-Based Batteries

TABLE 1 Battery Temperature Battery Voltage (° C.) (V/cell) <T₁ T₁ to T₂T₂ to T₃ >T₃ <V₁ No charge. Trickle charge. Trickle charge. No charge.Slow blink for first First LED on First LED on Slow blink for first LED.steady. steady. LED. V₁ to V₂ No charge. Step charge. Fast charge. Nocharge. Slow blink for first First LED on First LED on Slow blink forfirst LED. steady until near steady until near LED. full charge, thenfull charge, then turns off. turns off. Second LED blinks Second LEDblinks near full charge. near full charge. V₂ to V₃ No charge.Maintenance Maintenance No charge. Slow blink for first charge. charge.Slow blink for first LED. Second LED on Second LED on LED. steady.steady. >V₃ No charge. No charge. No charge. No charge. Fast blink forfirst Fast blink for first Fast blink for first Fast blink for firstLED. LED. LED. LED.

In some constructions and in some aspects, the charging current appliedto the battery 20 during the trickle charge module 215 includes applyinga full charge current (e.g., “I”) to the battery 20 for a first timeperiod, such as, for example, ten seconds, and then suspending the fullcharge current for a second time period, such as, for example, fiftyseconds. In some constructions, the full charge current is a pulse ofcharging current approximately at a predefined amplitude. In someconstructions, the battery charger 30 only enters the trickle chargemodule 215 if the battery voltage is less than a first predefinedvoltage threshold, V₁.

In some constructions and in some aspects, the charging current appliedto the battery 20 during the fast charge module 225 includes applyingthe full charge current to the battery 20 for a first time period, suchas, for example, one second, and then suspending the full charge currentfor a second time period, such as, for example, 50-ms. In someconstructions, the controller 100 sets a back-up timer to a firstpredefined time limit, such as, for example, approximately two hours. Inthese constructions, the battery charger 30 will not implement the fastcharge module 225 for the predefined time limit in order to avoidbattery damage. In other constructions, the battery charger 30 will shutdown (e.g., stop charging) when the predefined time limit expires.

In some constructions, the battery charger 30 only enters the fastcharge module 225 if the battery voltage is included in a range from thefirst voltage threshold, V₁, to a second predefined voltage threshold,V₂, and the battery temperature falls within a range from a secondbattery temperature threshold, T₂, to a third battery temperaturethreshold, T₃. In some constructions, the second voltage threshold, V₂,is greater than the first voltage threshold, V₁, and the thirdtemperature threshold, T₃, is greater than the second temperaturethreshold, T₂.

In some constructions and in some aspects, the charging current appliedto the battery 20 during the step charge module 220 includes applyingthe charging current of the fast charge module 225 to the battery 20,but having a duty cycle of one minute charging (“ON”), one minutesuspended charging (“OFF”). In some constructions, the controller 100sets a back-up timer to a second predefined time limit, such as, forexample, approximately four hours. In these constructions, the batterycharger 30 will not implement the step charge module 220 for thepredefined time limit in order to avoid battery damage.

In some constructions, the battery charger 30 only enters the stepcharge module 220 if the battery voltage is included in a range from thefirst voltage threshold, V₁, to the second voltage threshold, V₂, andthe battery temperature falls within a range from the first temperaturethreshold, T₁, to the second temperature threshold, T₂. In someconstructions, the second voltage threshold, V₂, is greater than thefirst voltage threshold, V₁, and the second temperature threshold, T₂,is greater than the first temperature threshold, T₁.

In some constructions and in some aspects, the charging current appliedto the battery 20 during the maintenance module 230 includes applying afull charge current to the battery 20 only when the battery voltagefalls to a certain predefined threshold. In some constructions, thethreshold is approximately 4.05-V/cell+/−1% per cell. In someconstructions, the battery charger 30 only enters the maintenance module230 if the battery voltage is included in the range of the secondvoltage threshold, V₂, to the third voltage threshold, V₃, and thebattery temperature falls within a range from the first temperaturethreshold, T₁, to the third temperature threshold, T₃.

In some constructions and in some aspects, the controller 100 implementsthe various charging modules 220-230 based on various batteryconditions. In some constructions, each charging module 220-230 includesthe same charging algorithm (e.g., algorithm for applying the fullcharge current). However, each charging module 220-230 implements,repeats or incorporates the charging algorithm in a different manner. Anexample of a charging algorithm is the charge current algorithmillustrated in flowchart 250 of FIG. 12, as will be discussed below.

As illustrated in FIGS. 5 a and 5 b, the charging operation 200 beginswhen a battery, such as the battery 20, is inserted or electricallyconnected to the battery charger 30 at step 305. At step 310, thecontroller 100 determines if a stable input of power, such as, forexample, the power source 130, is applied or connected to the batterycharger 30. As indicated in FIG. 5 a, the same operation (i.e., step 305proceeding to step 310) still applies if power is applied after thebattery 20 is electrically connected to the battery charger 30.

If the controller 100 determines there is not a stable input of powerapplied, then the controller 100 does not activate the indicator 110 andno charge is applied to the battery 20 at step 315. In someconstructions, the battery charger 30 draws a small discharge current atstep 315. In some constructions, the discharge current is approximatelyless than 0.1-mA.

If the controller 100 determines there is a stable input of powerapplied to the battery charger 30 at step 310, then the operation 200proceeds to step 320. At step 320, the controller 100 determines if allthe connections between the battery terminals 45, 50 and 55 and thebattery charger terminals 80, 85 and 90 are stable. If the connectionsare not stable at step 320, the controller 100 continues to step 315.

If the connections are stable at step 320, the controller 100 identifiesthe chemistry of the battery 20 via the sense terminal 55 of the battery20 at step 325. In some constructions, a resistive sense lead from thebattery 20, as sensed by the controller 100, indicates that the battery20 has a chemistry of either NiCd or NiMH. In some constructions, thecontroller 100 will measure the resistance of the resistive sense leadto determine the chemistry of the battery 20. For example, in someconstructions, if the resistance of the sense lead falls in a firstrange, then the chemistry of the battery 20 is NiCd. If the resistanceof the sense lead falls in a second range, then the chemistry of thebattery 20 is NiMH.

In some constructions, NiCd batteries and NiMH batteries are charged bythe battery charger 30 using a single charging algorithm that isdifferent from a charging algorithm implemented for batteries havingLi-based chemistries. In some constructions, the single chargingalgorithm for NiCd and NiMH batteries is, for example, an existingcharging algorithm for NiCd/NiMH batteries. In some constructions, thebattery charger 30 uses the single charging algorithm for charging NiCdbatteries and NiMH batteries but ends the charging process for NiCdbatteries with a different termination scheme than the terminationscheme used to terminate charging for NiMH batteries. In someconstructions, the battery charger 30 terminates charging for NiCdbatteries when a negative change in the battery voltage (e.g., −ΔV) isdetected by the controller 100. In some constructions, the batterycharger 30 terminates charging for NiMH batteries when a change inbattery temperature over time (e.g., ΔT/dt) reaches or exceeds apredefined termination threshold.

In some constructions, the NiCd and/or NiMH batteries are charged usinga constant current algorithm. For example, the battery charger 30 caninclude the same charging circuitry for charging different batterieshaving differing battery chemistries, such as NiCd, NiMH, Li-ion, andthe like. In an exemplary construction, the charger 30 can use thecharging circuitry to apply the same full charge current to NiCd andNiMH batteries as Li-ion batteries using a constant current algorithminstead of pulse charging. In another exemplary construction, thebattery charger 30 can be capable of scaling the full charge currentthrough the charging circuitry according to the battery chemistry.

In other constructions, the controller 100 does not determine the exactchemistry of the battery 20. Rather, the controller 100 implements acharging module that can effectively charge both NiCd batteries and NiMHbatteries.

In other constructions, the resistance of the sense lead could indicatethat the battery 20 has a Li-based chemistry. For example, if theresistance of the sense lead falls in a third range, then the chemistryof the battery 20 is Li-based.

In some constructions, a serial communication link between the batterycharger 30 and the battery 20 established through the sense terminals 55and 90 indicates that the battery 20 has a Li-based chemistry. If aserial communication link is established at step 320, then amicroprocessor or controller, such as the controller 64, in the battery20 sends information regarding the battery 20 to the controller 100 inthe battery charger 30. Such information transferred between the battery20 and battery charger 30 can include battery chemistry, nominal batteryvoltage, battery capacity, battery temperature, individual cellvoltages, number of charging cycles, number of discharging cycles,status of a protection circuit or network (e.g., activated, disabled,enabled, etc.), etc.

At step 330, the controller 100 determines if the chemistry of thebattery 20 is Li-based or not. If the controller 100 determines that thebattery 20 has a chemistry of either NiCd or NiMH at step 330, then theoperation 200 proceeds to the NiCd/NiMH charging algorithm at step 335.

If the controller 100 determines that the battery 20 has a chemistrythat is Li-based at step 330, then the operation 200 proceeds to step340. At step 340, the controller 100 resets any battery protectioncircuit, such as, for example, a switch, included in the battery 20 anddetermines the nominal voltage of the battery 20 via the communicationlink. At step 345, the controller 100 sets the charger analog-to-digitalconverter (“A/D”) to the appropriate level based on nominal voltage.

At step 350, the controller 100 measures the present voltage of thebattery 20. Once a measurement is made, the controller 100 determines ifthe voltage of the battery 20 is greater than 4.3-V/cell at step 355. Ifthe battery voltage is greater than 4.3-V/cell at step 355, then theoperation 200 proceeds to the defective pack module 205 at step 360. Thedefective pack module 205 will be discussed below.

If the battery voltage is not greater than 4.3-V/cell at step 355, thenthe controller 100 measures the battery temperature at step 365 anddetermines if the battery temperature falls below −10° C. or exceeds 65°C. at step 370. If the battery temperature is below −10° C. or is above65° C. at step 370, then the operation 200 proceeds to the temperatureout-of-range module 210 at step 375. The temperature out-of-range module210 will be discussed below.

If the battery temperature is not below −10° C. or does not exceed 65°C. at step 370, then the controller 100 determines at step 380 (shown inFIG. 5 b) if the battery temperature falls between −10° C. and 0° C. Ifthe battery temperature falls between −10° C. and 0° C. at step 380, theoperation 200 proceeds to step 385. At step 385, the controller 100determines if the battery voltage is less than 3.5-V/cell. If thebattery voltage is less than 3.5-V/cell, the operation 200 proceeds tothe trickle charge module 215 at step 390. The trickle charge module 215will be discussed below.

If the battery voltage is not less than 3.5-V/cell at step 385, thecontroller 100 determines if the battery voltage is included in thevoltage range of 3.5-V/cell to 4.1-V/cell at step 395. If the batteryvoltage is not included in the voltage range of 3.5-V/cell to 4.1-V/cellat step 395, then the operation 200 proceeds to the maintenance module230 at step 400. The maintenance module 230 will be discussed below.

If the battery voltage is included in the voltage range of 3.5-V/cell to4.1-V/cell at step 395, the controller 100 clears a counter, such as acharge counter, at step 405. Once the charge counter is cleared at step405, the operation 200 proceeds to the step charge module 220 at step410. The step charge module 220 and charge counter will be discussedbelow.

Referring back to step 380, if the battery temperature is not includedwithin the range of −10° C. and 0° C., the controller 100 determines ifthe battery voltage is less than 3.5-V/cell at step 415. If the batteryvoltage is less than 3.5-V/cell at step 415, the operation 200 proceedsto the trickle charge module 215 at step 420.

If the battery voltage is not less than 3.5-V/cell at step 415, thecontroller 100 determines if the battery voltage is included in thevoltage range of 3.5-V/cell to 4.1-V/cell at step 425. If the batteryvoltage is not included in the voltage range of 3.5V/cell to 4.1-V/cellat step 425, then the operation 200 proceeds to the maintenance module230 at step 430.

If the battery voltage is included in the voltage range of 3.5-V/cell to4.1-V/cell at step 425, the controller 100 clears a counter, such as thecharge counter, at step 435. Once the charge counter is cleared at step435, the operation 200 proceeds to the fast charge module 225 at step440. The fast charge module 225 will be discussed below.

FIG. 6 is a flowchart illustrating the operation of the defective packmodule 205. Operation of the module 205 begins when the main chargingoperation 200 enters the defective pack module 205 at step 460. Thecontroller 100 interrupts the charging current at step 465 and activatesthe indicator 110, such as the first LED, at step 470. In theillustrated construction, the controller 100 controls the first LED toblink at a rate of approximately 4-Hz. Once the indicator 110 isactivated in step 470, the module 205 ends at step 475, and theoperation 200 may also end.

FIG. 7 is a flowchart illustrating the operation of the temperatureout-of-range module 210. Operation of the module 210 begins when themain charging operation 200 enters the temperature out-of-range module210 at step 490. The controller 100 interrupts the charging current atstep 495 and activates the indicator 110, such as the first LED, at step500. In the construction illustrated, the controller 100 controls thefirst LED to blink at a rate of approximately 1-Hz to indicate to a userthat the battery charger 30 is currently in the temperature-out-of-rangemodule 210. Once the indicator 110 is activated in step 500, operation200 exits the module 210 and proceeds to where the operation 200 leftoff.

FIG. 8 is a flowchart illustrating the trickle charge module 215.Operation of the module 215 begins when the main charging operation 200enters the trickle charge module 215 at step 520. The controller 100activates the indicator 110, such as the first LED 115, at step 525 toindicate to a user that the battery charger 30 is currently charging thebattery 20. In the illustrated construction, the controller 100activates the first LED 115 so that it appears to be constantly on.

Once the indicator 110 is activated in step 525, the controller 100initializes a counter, such as a trickle charge count counter, at step530. In the construction illustrated, the trickle charge count counterhas a count limit of twenty.

At step 540, the controller 100 begins to apply ten one second (“1-s”)full current pulses to the battery 20 and then suspends charging forfifty seconds (“50-s”). In some constructions, there are 50-ms timeintervals between the 1-s pulses.

At step 545, the controller 100 measures the battery voltage when acharging current is applied to the battery 20 (e.g., current on-times)to determine if the battery voltage exceeds 4.6-V/cell. If the batteryvoltage exceeds 4.6-V/cell during current on-times at step 545, themodule 215 proceeds to the defective pack module 205 at step 550 andwould end at step 552. If the battery voltage does not exceed 4.6-V/cellduring current on-times at step 545, the controller 100 measures thebattery temperature and the battery voltage when a charging current isnot applied to the battery 20 (e.g., current off-times) at step 555.

At step 560, the controller 100 determines if the battery temperaturefalls below −10° C. or exceeds 65° C. If the battery temperature isbelow −10° C. or is above 65° C. at step 560, then the module 215proceeds to the temperature out-of-range module 210 at step 565 andwould end at step 570. If the battery temperature is not below −10° C.or is not above 65° C. at step 560, then the controller 100 determinesif the battery voltage is included in the range of 3.5-V/cell to4.1-V/cell at step 575.

If the battery voltage is included in the range of 3.5-V/cell to4.1-V/cell at step 575, then the controller 100 determines if thebattery temperature is included in the range of −10° C. to 0° C. at step580. If the battery temperature is included in the range of −10° C. to0° C. at step 580, then the module 215 proceeds to the step chargemodule 220 at step 585. If the battery temperature is not included inthe range of −10° C. to 0° C. at step 580, then the module 215 proceedsto the fast charge module 225 at step 590.

If the battery voltage is not included in range of 3.5-V/cell to4.1-V/cell at step 575, then the controller 100 increments the tricklecharge count counter at step 595. At step 600, the controller 100determines if the trickle charge count counter equals the counter limit,such as for example, twenty. If the counter does not equal the counterlimit at step 600, the module 215 proceeds to step 540. If the counterdoes equal the count limit at step 600, the module 215 proceeds to thedefective pack module 205 at step 605 and would end at step 610.

FIG. 9 is a flowchart illustrating the step charge module 220. Operationof the module 220 begins when the main charging operation 200 enters thestep charge module 220 at step 630. The controller 100 activates theindicator 110, such as the first LED 115, at step 635 to indicate to auser that the battery charger 30 is currently charging the battery 20.In the illustrated construction, the controller 100 activates the firstLED 115 so that it appears to be constantly on.

At step 640, the controller 100 starts a first timer or charge-on timer.In the illustrated construction, the charge-on timer counts down fromone minute. At step 645, the module 220 proceeds to the charge currentalgorithm 250. Once the charge current algorithm 250 is performed, thecontroller 100 determines if the charge count equals the count limit,such as, for example, 7,200, at step 650. If the charge count equals thecount limit at step 650, the module 220 proceeds to the defective packmodule 205 at step 655 and the module 220 would end at step 660.

If the charge count does not equal the count limit at step 650, thecontroller 100 determines if the waiting time between current pulses (aswill be discussed below) is greater than or equal to a first waitingtime threshold, such as, for example, two seconds, at step 665. If thewaiting time is greater than or equal to the first waiting timethreshold at step 665, the controller 100 activates the indicator 110 atstep 670, such as, for example, turns off the first LED 115 andactivates the second LED 120 to blink at approximately 1-Hz. If thewaiting time is not greater than or equal to the first waiting timethreshold at step 665, the module 220 proceeds to step 690, which isdiscussed below.

Once the indicator 110 is activated at step 670, the controller 100determines if the waiting time between current pulses is greater than orequal to a second waiting time threshold, such as, for example, fifteenseconds, at step 675. If the waiting time is greater than or equal tothe second waiting time threshold at step 675, the controller 100changes the indicator 110 at step 680, such as, for example, activatesthe second LED 120 such that the second LED 120 appears to be onconstantly. The module 220 then proceeds to the maintenance module 230at step 685.

If the waiting time is not greater than or equal to the second waitingtime threshold at step 675, the controller 100 determines if the batterytemperature is greater than 0° C. at step 690. If the batterytemperature is greater than 0° C. at step 690, the module 220 proceedsto the fast charge module 225 at step 695. If the battery temperature isnot greater than 0° C. at step 690, the controller 100 determines if thecharge-on timer has expired at step 700.

If the charge-on timer has not expired at step 700, the module 220proceeds to the charge current algorithm 250 at step 645. If thecharge-on timer has expired at step 700, the controller 100 activates asecond timer or a charge-off timer at step 705 and suspends charging. Atstep 710, the controller 100 determines if the charge-off timer hasexpired. If the charge-off timer has not expired at step 710, thecontroller 100 waits for a predefined amount of time at step 715 andthen proceeds back to step 710. If the charge-off timer has expired atstep 710, the module 220 proceeds back to step 640 to start thecharge-on timer again.

FIG. 10 is a flowchart illustrating the fast charge module 225.Operation of the module 225 begins when the main charging operation 200enters the fast charge module 220 at step 730. The controller 100activates the indicator 110, such as the first LED 115, at step 735 toindicate to a user that the battery charger 30 is currently charging thebattery 20. In the illustrated construction, the controller 100activates the first LED 115 so that it appears to be constantly on.

At step 740, the module 225 proceeds to the charge current algorithm250. Once the charge current algorithm 250 is performed, the controller100 determines if the charge count equals the count limit (e.g., 7,200)at step 745. If the charge count equals the count limit at step 650, themodule 220 proceeds to the defective pack module 205 at step 750 and themodule 220 would end at step 755.

If the charge count does not equal the count limit at step 745, thecontroller 100 determines if the waiting time between current pulses isgreater than or equal to the first waiting time threshold (e.g., twoseconds) at step 760. If the waiting time is greater than or equal tothe first waiting time threshold at step 760, the controller 100activates the indicator 110 at step 765, such as, for example, turns offthe first LED 115 and activates the second LED 120 to blink atapproximately 1-Hz. If the waiting time is not greater than or equal tothe first waiting time threshold at step 760, the module 225 proceeds tostep 785, which is discussed below.

Once the indicator 110 is activated at step 765, the controller 100determines if the waiting time between current pulses is greater than orequal to a second waiting time threshold (e.g., fifteen seconds) at step770. If the waiting time is greater than or equal to the second waitingtime threshold at step 770, the controller 100 changes the indicator 110at step 775, such as, for example, activates the second LED 120 suchthat the second LED 120 appears to be on constantly. The module 225 thenproceeds to the maintenance module 230 at step 780.

If the waiting time is not greater than or equal to the second waitingtime threshold at step 770, the controller 100 determines if the batterytemperature is included in the range of −20° C. to 0° C. at step 785. Ifthe battery temperature is included in the range at step 785, the module225 proceeds to the step charge module 220 at step 790. If the batterytemperature is not included in the range at step 785, the module 225proceeds back to the charge current algorithm 250 at step 740.

FIG. 11 is a flowchart illustrating the maintenance module 230.Operation of the module 230 begins when the main charging operation 200enters the maintenance module 230 at step 800. The controller 100determines is the battery voltage is included within the range of3.5-V/cell to 4.05-V/cell at step 805. If the battery voltage is notincluded in the range at step 805, the controller 100 continues to stayin step 805 until the battery voltage is included in the range. Once thebattery voltage is included in the range at step 805, the controller 100initializes a maintenance timer at step 810. In some constructions, themaintenance timer counts down from thirty minutes.

At step 815, the controller 100 determines if the battery temperaturefalls below −20° C. or exceeds 65° C. If the battery temperature fallsbelow −20° C. or exceeds 65° C. at step 815, the module 230 proceeds tothe temperature out-of-range module 210 at step 820 and the module wouldend at step 825. If the battery temperature does not fall below −20° C.or does not exceed 65° C. at step 815, the module 230 proceeds to thecharge current algorithm 250 at step 830.

Once the charge current algorithm 250 is performed at step 830, thecontroller 100 determines if the maintenance timer has expired at step835. If the maintenance timer has expired, the module 230 proceeds tothe defective pack module 840 at step 840, and the module 230 would endat step 845. If the maintenance timer has not expired at step 835, thecontroller 100 determines if the waiting time between the current pulsesis greater than or equal to a first predefined maintenance waiting timeperiod, such as, for example, fifteen seconds, at step 850.

If the waiting time is greater than the first predefined maintenancewaiting time period at step 850, the module 230 proceeds to step 805. Ifthe waiting time is not greater than or equal to the first predefinedmaintenance waiting time period at step 850, the module 230 proceeds tothe charge current algorithm 250 at step 830. In some constructions, thebattery charger 30 will remain in the maintenance module 230 until thebattery pack 20 is removed from the battery charger 30.

FIG. 12 is a flowchart illustrating the base charge scheme or chargecurrent algorithm 250. Operation of the module 250 begins when the othermodules 220-230 or main charging operation 200 enters the charge currentalgorithm 250 at step 870. The controller 100 applies a full currentpulse for approximately one second at step 875. At step 880, thecontroller 100 determines if the battery voltage 880 is greater than4.6-V/cell when current is being applied to the battery 20.

If the battery voltage is greater than 4.6-V/cell at step 880, then thealgorithm 250 proceeds to the defective pack module 205 at step 885, andthe algorithm 250 would end at step 890. If the battery voltage is notgreater than 4.6-V/cell at step 880, the controller 100 interrupts thecharging current, increments a counter, such as the charge currentcounter, and stores the count value at step 895.

At step 900, the controller 100 determines is the battery temperaturefalls below −20° C. or exceeds 65° C. If the battery temperature fallsbelow −20° C. or exceeds 65° C. at step 900, the algorithm 250 proceedsto the temperature out-of-range module 205 at step 905, and thealgorithm 250 will terminate at step 910. If the battery temperaturedoes not fall below −20° C. or does not exceed 65° C. at step 900, thecontroller 100 measures the battery voltage when the charging current isnot being supplied to the battery 20 at step 915.

At step 920, the controller 100 determines if the battery voltage isless than 4.2-V/cell. If the battery voltage is less than 4.2-V/cell atstep 920, the algorithm 250 proceeds to step 875. If the battery voltageis not less than 4.2-V/cell at step 920, the controller 100 waits untilthe battery voltage approximately equals 4.2-V/cell at step at 925. Alsoat step 925, the controller 100 stores the waiting time. The algorithm250 ends at step 930.

In another construction, the full charge current or full charge pulseapplied by the battery charger 30 can be scaled according to theindividual cell voltages in the battery 20. This implementation will bedescribed with respect to FIGS. 4 and 16.

As shown in FIG. 4, the controller 100 in the battery charger 30 canreceive and transmit information from and to the microcontroller 64 inthe battery 20. In some constructions, the microcontroller 64 canmonitor various battery characteristics during charging, including thevoltages or present state of charge of each battery cells 60, eitherautomatically or in response to a command from the battery charger 30.The microcontroller 64 can monitor certain battery characteristics andprocess or average measurements during periods of charge current (i.e.,“current on” time periods) T_(on). In some constructions, the current ontime period can be approximately one second (“1-s”). During periods ofno charge current (i.e., “current off” time periods) T_(off),information regarding certain battery characteristics (e.g., cellvoltages or cell state of charges) can be transferred from the battery20 to the charger 30. In some constructions, the current off time periodT_(off) is approximately 50 ms. The battery charger 30 can process theinformation sent from the battery 20 and modify the current on timeperiods T_(on) accordingly. For example, if one or more battery cells 60have a higher present state of charge than the remaining battery cells60, then the battery charger 30 may decrease subsequent current on timeperiods T_(on) in order to avoid overcharging the one or more higherbattery cells.

In some constructions, the battery charger 30 may compare eachindividual cell voltage to an average cell voltage, and if thedifference between the individual cell voltage and the average cellvoltage equals or exceeds a predefined threshold (e.g., an imbalancethreshold) then the charger 30 may identify the cell as being a higherstate of charge cell. The battery charger 30 may modify the current ontime period T_(on). In other constructions, the battery charger 30 mayestimate the state of charge for a particular battery cell (such as abattery cell identified as a higher voltage cell) during current on timeperiods based on the information received from the battery 20. In theseconstructions, if the estimation of the present state of charge for thecell exceeds a threshold, then the battery charger 30 may modify theduration of the current on time period T_(on).

For example, as shown in FIG. 16, the battery charger 30 can command thebattery 20 to average the cell voltage measurements taken during thenext current on time T_(on1). The command may be sent during the firstcurrent off time period T_(off1). Accordingly, during the first currenton time T_(on1), the microcontroller 64 measures and averages the cellvoltages as well as other battery parameters. During the next currentoff time T_(off1), the battery 30 can transmit the averaged measurementsto the battery charger 30. In some constructions, the battery 20 cansend eight averaged measurements such as, for example, an averaged packstate of charge measurement and an averaged individual cell state ofcharge for each of the seven battery cells 60. For example, the battery20 may send the following information: cell 1 14%, cell 2 14%, cell 315%, cell 4 14%, cell 5 16%, cell 6 14%, cell 7 14%, and pack (e.g.,cells 1-7) voltage 29.96 V. In this example, the battery charger 30identifies cell 5 as being a higher battery cell. The charger 30 alsorecords the battery voltage as measured by the both the batterymicrocontroller 64 and the battery charger 30. In this example, thebattery charger 30 measures the battery voltage as approximately 30.07V. The battery charger 30 computes the difference in battery voltagemeasurements (e.g., 110 mV), and determines the voltage drop across theterminals and leads as approximately 110 mV.

During the subsequent current on time period T_(on2), the batterycharger 30 “estimates” the voltage of cell 5. For example, the batterycharger 30 samples measurements of the voltage of the battery 20, andfor each battery voltage measurement, estimates the state of charge forcell 5 according to the following equation:(V_(battery/ch)−V_(terminals))*V_(cell)wherein V_(battery/ch) is the voltage of the battery 20 as measurementby the charger 30, V_(terminals) is the voltage drop across theterminals (e.g., 110 mV), and V_(cell) is the voltage of the cell beingestimated as a percentage of the battery voltage. If the estimation ofcell 5's voltage exceeds a threshold, then the battery charger 30 maymodify the subsequent current on time period T_(on3). As shown in FIG.16, the charger 30 identifies cell 5 as being a high battery cell, andmodifies the subsequent current on time period T_(on3) to beapproximately 800 ms. Accordingly, the length T₂ of the current on timeperiod T_(on3) is less than the length T₁ of the previous current ontime periods T_(on1) and T_(on2).

In some constructions, the charger 30 continues to set the subsequentcurrent on time periods (e.g., T_(on4-5)) to approximately the length T₂of the previous current on time period T_(on3) (e.g., 800 ms). If cell 5(or another cell) continues to be identified as a high cell, then thecharger 30 can modify the length the subsequent current on time period(e.g., T_(on6)) from length T₂ (e.g., approximately 800 ms) to T₃ (e.g.,approximately 600 ms), for example.

A further schematic diagram of a battery 20′ is schematicallyillustrated in FIG. 13. The battery 20′ is similar to the battery 20,and common elements are identified by the same reference number “′”.

In some constructions, the circuit 62′ includes an electrical componentsuch as, for example, an identification resistor 950, and theidentification resistor 950 can have a set resistance. In otherconstructions, the electrical component may be a capacitor, an inductor,a transistor, a semiconducting element, an electrical circuit or anothercomponent having a resistance or capable of sending an electrical signalsuch as, for example, a microprocessor, a digital logic component andthe like. In the illustrated construction, the resistance value of theidentification resistor 950 can be chosen based on characteristics ofthe battery 20′, such as the nominal voltage and the chemistry of thebattery cell(s) 60′. A sense terminal 55′ can electrically connect tothe identification resistor 950.

The battery 20′, shown schematically in FIG. 13, can electricallyconnect to an electrical device, such as a battery charger 960 (alsoshown schematically). The battery charger 960 can include a positiveterminal 964, a negative terminal 968 and a sense terminal 972. Eachterminal 964, 968, 972 of the battery charger 960 can electricallyconnect to the corresponding terminal 45′, 50′, 55′ (respectively), ofthe battery 20′. The battery charger 960 also can include a circuithaving electrical components, such as, for example, a first resistor976, a second resistor 980, a solid-state electronic device orsemiconductor 984, a comparator 988 and a processor, microcontroller orcontroller (not shown). In some constructions, the semiconductor 984 caninclude a transistor capable of operating in saturation or an “ON” stateand capable of operating in cut-off or an “OFF” state. In someconstructions, the comparator 988 can be a dedicated voltage monitoringdevice, a microprocessor or a processing unit. In other constructions,the comparator 988 can be included in the controller (not shown).

In some constructions, the controller (not shown) can be programmed toidentify the resistance value of the electrical component in the battery20′, such as the identification resistor 958. The controller can also beprogrammed to determine one or more characteristics of the battery 20′,such as, for example, the battery chemistry and the nominal voltage ofthe battery 20′. As previously mentioned, the resistance value of theidentification resistor 958 may correspond to a dedicated valueassociated with one or more certain battery characteristics. Forexample, the resistance value of the identification resistor 958 can beincluded in a range of resistance values corresponding to the chemistryand to the nominal voltage of the battery 20′.

In some constructions, the controller can be programmed to recognize aplurality of resistance ranges of the identification resistor 958. Inthese constructions, each range corresponds to one battery chemistry,such as, for example, NiCd, NiMH, Li-ion, and the like. In someconstructions, the controller can recognize additional resistanceranges, each corresponding to another battery chemistry or anotherbattery characteristic.

In some constructions, the controller can be programmed to recognize aplurality of voltage ranges. The voltages included in the voltage rangescan be dependent on or correspond to the resistance value of theidentification resistor 958, such that the controller can determine thevalue of the resistor 958 based on the measured voltage.

In some constructions, the resistance value of the identificationresistor 958 can be further chosen to be unique for each possiblenominal voltage value of the battery 20′. For example, in one range ofresistance values, a first dedicated resistance value can correspond toa nominal voltage of 21 V, a second dedicated resistance value cancorrespond to a nominal voltage of 16.8 V, and a third dedicatedresistance value can correspond to a nominal voltage of 12.6 V. In someconstructions, there can be more or fewer dedicated resistance values,each corresponding to another possible nominal voltage of the battery20′ associated with the resistance range.

In an exemplary implementation, the battery 20′ electrically connects tothe battery charger 960. To identify a first battery characteristic, thesemiconductor 984 switches to the “ON” state under the control ofadditional circuitry (not shown). When the semiconductor 984 is in the“ON” state, the identification resistor 958 and resistors 976 and 980create a voltage divider network. The network establishes a voltageV_(A) at a first reference point 992. If the resistance value of theresistor 980 is significantly lower than the resistance value of theresistor 976, then the voltage V_(A) will be dependent upon theresistance values of the identification resistor 958 and the resistor980. In this implementation, the voltage V_(A) is in a range determinedby the resistance value of the identification resistor 958. Thecontroller (not shown) measures the voltage V_(A) at the first referencepoint 992 and determines the resistance value of the identificationresistor 958 based on the voltage V_(A). In some constructions, thecontroller compares the voltage V_(A) to a plurality of voltage rangesto determine the battery characteristic.

In some constructions, the first battery characteristic to be identifiedcan include the battery chemistry. For example, any resistance valuebelow 150 k ohms may indicate that the battery 20′ has a chemistry ofNiCd or NiMH, and any resistance value approximately 150 k ohms or abovemay indicate that the battery 20′ has a chemistry of Li or Li-ion. Oncethe controller determines and identifies the chemistry of the battery20′, an appropriate charging algorithm or method may be selected. Inother constructions, there are more resistance ranges which eachcorrespond to another battery chemistry than in the above example.

Continuing with the exemplary implementation, to identify a secondbattery characteristic, the semiconductor 984 switches to the “OFF”state under the control of the additional circuitry. When thesemiconductor 984 switches to the “OFF” state, the identificationresistor 958 and the resistor 976 create a voltage divider network. Thevoltage V_(A) at the first reference point 992 is now determined by theresistance values of the identification resistor 958 and the resistor976. The resistance value of the identification resistor 958 is chosensuch that, when the voltage V_(BATT) at a second reference point 880substantially equals the nominal voltage of the battery 20′, the voltageV_(A) at the first reference point 992 substantially equals a voltageV_(REF) at a third reference point 996. If the voltage V_(A) at thefirst reference point 992 exceeds the fixed voltage V_(REF) at the thirdreference point 996, an output V_(OUT) of the comparator 988 changesstate. In some constructions, the output V_(OUT) can be used toterminate charging or to serve as an indicator to commence additionalfunctions, such as a maintenance routine, an equalization routine, adischarging function, additional charging schemes, and the like. In someconstructions, voltage V_(REF) can be a fixed reference voltage.

In some constructions, the second battery characteristic to beidentified can include a nominal voltage of the battery 20′. Forexample, a general equation for calculating the resistance value for theidentification resistor 958 can be:

$R_{100} = \frac{V_{REF} \cdot R_{135}}{V_{BATT} - V_{REF}}$wherein R₁₀₀ is the resistance value of the identification resistor 958,R₁₃₅ is the resistance value of the resistor 976, V_(BATT) is thenominal voltage of the battery 20′ and V_(REF) is a fixed voltage, suchas, for example, approximately 2.5 V. For example, in the range ofresistance values for the Li-ion chemistry (set forth above), aresistance value of approximately 150 k ohms for the identificationresistor 958 can correspond to a nominal voltage of approximately 21 V,a resistance value of approximately 194 k ohms can correspond to anominal voltage of approximately 16.8 V, and a resistance value ofapproximately 274.7 k ohms can correspond to a nominal voltage ofapproximately 12.6 V. In other constructions, more or fewer dedicatedresistance values may correspond to additional or different battery packnominal voltage values.

In the illustrated construction, both the identification resistor 958and the third reference point 996 may be situated on the “high” side ofa current sense resistor 1000. Positioning the identification resistor958 and the third reference point 996 in this manner can reduce anyrelative voltage fluctuations between V_(A) and V_(REF) when a chargingcurrent is present. Voltage fluctuations may appear in voltage V_(A) ifthe identification resistor 958 and the third reference point 996 werereferenced to ground 1004 and a charging current was applied to thebattery 20′.

In some constructions, the battery charger 960 can also include acharger control function. As previously discussed, when the voltageV_(A) substantially equals the voltage V_(REF) (indicative of voltageV_(BATT) equaling the nominal voltage of battery 20′), the outputV_(OUT) of the comparator 988 changes state. In some constructions, thecharging current is no longer supplied to the battery 20′ when theoutput V_(OUT) of the comparator 988 changes state. Once the chargingcurrent is interrupted, the battery voltage V_(BATT) begins to decrease.When voltage V_(BATT) reaches a low threshold, the output V_(OUT) of thecomparator 860 changes state again. In some constructions, the lowthreshold of voltage V_(BATT) is determined by a resistance value of ahysteresis resistor 1008. The charging current is reestablished once theoutput V_(OUT) of the comparator 988 changes state again. In someconstructions, this cycle repeats for a predefined amount of time asdetermined by the controller or repeats for a certain amount of statechanges made by the comparator 988. In some constructions, this cyclerepeats until the battery 20′ is removed from the battery charger 960.

In some constructions and in some aspects, a battery, such as thebattery 20 shown in FIG. 17, can become so discharged that the batterycells 60 may not have enough voltage to communicate with a batterycharger 30. As shown in FIG. 17, the battery 20 can include one or morebattery cells 60, a positive terminal 1105, a negative terminal 1110 andone or more sense terminals 1120 a and 1120 b (as shown in FIG. 17, thesecond sense terminal or activation terminal 120 b may or may not beincluded in the battery 20). The battery 20 can also include a circuit1130 including a microcontroller 1140.

As shown in FIG. 17, the circuit 1130 can include a semiconductingswitch 1180 that interrupts the discharging current when the circuit1130 (e.g., the microprocessor 1140) determines or senses a conditionabove or below a predetermined threshold (i.e., an “abnormal batterycondition”). In some constructions, the switch 1180 includes aninterruption condition in which current from or to the battery 20 isinterrupted, and an allowance condition in which current from or to thebattery 20 is allowed. In some constructions, an abnormal batterycondition can include, for example, high or low battery celltemperature, high or low battery state of charge, high or low batterycell state of charge, high or low discharge current, high or low chargecurrent, and the like. In the illustrated constructions, the switch 1180includes a power FET or a metal-oxide semiconductor FET (“MOSFET”). Inother constructions, the circuit 1130 can include two switches 1180. Inthese constructions, the switches 1180 can be arranged in parallel.Parallel switches 1180 can be included in battery packs supplying a highaverage discharge current (such as, for example, the battery 20supplying power to a circular saw, a driver drill, and the like).

In some constructions, once the switch 1180 becomes non-conducting, theswitch 1180 may not reset even if the abnormal condition is no longerdetected. In some constructions, the circuit 1130 (e.g., themicroprocessor 1140) may reset the switch 180 only if an electricaldevice, such as, for example, a battery charger 30, instructs themicroprocessor 1140 to do so. As mentioned previously, the battery 20may become so discharged that the battery cells 60 may not have enoughvoltage in order to power the microprocessor 1140 to communicate with abattery charger 30.

In some constructions, if the battery 20 cannot communicate with thecharger 30, the battery charger 30 can supply a small charge currentthough the body diode 1210 of the switch 1180 to slowly charge thebattery cells 60. Once the cells 60 receive enough charge current topower the microprocessor 1140, the microprocessor 1140 can change thestate of the switch 1180. That is, the battery 50 can be charged evenwhen the switch 1180 is in the non-conducting state. As shown in FIG.17, the switch 180 can include the body diode 1210, which, in someconstructions, is integral with a MOSFET and other transistors. In otherconstructions, the diode 1210 can be electrically connected in parallelwith the switch 1180.

In some constructions, if the battery 20 cannot communicate with thecharger 30, the battery charger 30 can apply a small average currentthrough a sense lead such as, for example, the sense lead 120 a or thededicated activation terminal 120 b. The current may charge a capacitor1150, which in turn can supply enough voltage to the microprocessor 1140to enable operation.

The constructions described above and illustrated in the figures arepresented by way of example only and are not intended as a limitationupon the concepts and principles of the present invention. As such, itwill be appreciated by one having ordinary skill in the art that variouschanges in the elements and their configuration and arrangement arepossible without departing from the spirit and scope of the presentinvention.

1. A battery charging system including a battery charger and a batterypack, the system comprising: a battery charger housing; at least oneterminal to electrically connect the battery charger to the batterypack, the battery pack supported by and removably mounted to the batterycharger housing, the battery pack including a plurality of lithium-basedbattery cells, each battery cell of the plurality of battery cellshaving an individual state of charge; and a controller within thebattery charger housing and operable to supply a charging current to thebattery pack through the at least one terminal, the controller beingoperable to control the charging current being supplied to the batterypack based at least in part on the individual state of charge of atleast one of the plurality of battery cells, wherein each battery cellof the plurality of battery cells is individually tapped such that thecontroller is operable to monitor the respective individual state ofcharge thereof.
 2. The system of claim 1, wherein the controller isfurther operable to supply a charging current to the battery pack bysupplying the charging current in a plurality of pulses of chargingcurrent, the plurality of pulses each having a first period of time, inwhich the charging current is being supplied to the battery pack at apredefined amplitude, and a second period of time, in which the supplyof charging current is suspended.
 3. The system of claim 2, wherein thecontroller is further operable to control the charging current beingsupplied to the battery pack by modifying at least one of the firstperiod of time and the second period of time.
 4. The system of claim 1,wherein the controller includes a first charging module and a secondcharging module, the first charging module being operable to provide afirst charging current to the battery pack, the second charging modulebeing operable to provide a second charging current to the battery pack,and wherein the controller implements one of the first charging moduleand the second charging module based at least in part on the individualstate of charge of the at least one battery cell.
 5. The system of claim4, wherein the first charging current and the second charging currentdiffer in one of average current amplitude and duty-cycle.
 6. The systemof claim 1, wherein the controller is further operable to control thecharging current being supplied to the battery pack based at least inpart on battery temperature.
 7. The system of claim 1, wherein thebattery cells have a lithium-manganese spinel chemistry.
 8. A batterycharging system including a battery charger and a power tool batterypack, the system comprising: a battery charger housing; at least threeterminals to electrically connect the battery charger to the power toolbattery pack, the power tool battery pack supported by and removablycoupled to the battery charger housing, the battery pack including aplurality of lithium-based battery cells, each battery cell of theplurality of battery cells having an individual state of charge; and acontroller within the battery charger housing and operable to supply acharging current to the battery pack through at least one of the threeterminals, the controller being operable to control the charging currentbeing supplied to the battery pack based at least in part on theindividual state of charge of at least one of the plurality batterycells, wherein each battery cell of the plurality of battery cells isindividually tapped such that the controller is operable to monitor therespective individual state of charge thereof via one of the terminals.9. The system of claim 8, wherein the controller is further operable tosupply a charging current to the battery pack by supplying the chargingcurrent in a plurality of pulses of charging current, the plurality ofpulses each having a first period of time, in which the charging currentis being supplied to the battery pack at a predefined amplitude, and asecond period of time, in which the supply of charging current issuspended.
 10. The system of claim 9, wherein the controller is furtheroperable to control the charging current being supplied to the batterypack by modifying at least one of the first period of time and thesecond period of time.
 11. The system of claim 8, wherein the controllerincludes a first charging module and a second charging module, the firstcharging module being operable to provide a first charging current tothe battery pack, the second charging module being operable to provide asecond charging current to the battery pack, and wherein the controllerimplements one of the first charging module and the second chargingmodule based at least in part on the individual state of charge of theat least one battery cell.
 12. The system of claim 11, wherein the firstcharging current and the second charging current differ in one ofaverage current amplitude and duty-cycle.
 13. The system of claim 8,wherein the controller is further operable to control the chargingcurrent being supplied to the battery pack based at least in part onbattery temperature.
 14. The system of claim 8, wherein the batterycells have a lithium-manganese spinel chemistry.
 15. The system of claim1, wherein the controller is further operable to compare the individualstate of charge of the at least one of the plurality of battery cells toan average state of charge for the plurality of battery cells.
 16. Thesystem of claim 8, wherein the controller is further operable to comparethe individual state of charge of the at least one of the plurality ofbattery cells to an average state of charge for the plurality of batterycells.